Questions about the cardio serie

Training Q&A [Moderated]
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Hi, I have some questions

In your cardio podcast, you mentioned that Zone 2 in a 5-zone model equals RPE 5–6, whereas I usually see it defined as RPE 3–4.Why is that? You also noted that endurance athletes do 80% of their training in Zones 1 and 2, which corresponds to RPE 1–4 if I am correct.

  • Intensity vs. Adaptation: You suggested that intensities below RPE 5–6—using walking as an example—might not be ideal for improving cardiovascular capacity and overall health. If that is the case, why do elite endurance athletes spend the majority of their training volume below that RPE?

  • Health Impact for Amateurs: For someone doing cardio 2–3h a week for exemple, would spending 80% of that time at RPE ≤4 versus RPE 5–6 result in fewer positive cardiovascular improvements and therefore health improvements ?

  • RPE vs. Heart Rate Mismatch: When I briskly walk at ~6 km/h, my RPE reaches 5–6, but my heart rate is only 100–110 bpm (53–58% of my estimated Max HR at age 26). This falls below Zone 1 (60–75% Max HR as you described) but my RPE says zone 3. Conversely, when I run at a 5:40/km pace, my HR is 140–150 bpm (74–79% Max HR, which you place in Zone 2), but my perceived exertion is an RPE 6–7. (For context, I’m physically active and have always played sports, including 14 years of hockey, though cardio was never my strong suit!).

  • Metric Choice: Should we rely more on RPE or % Max HR when training for conditioning?

Thanks

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Howdy!

To start, I think it’s important to note that there’s no standardized 5-zone model, no agreed-upon cutoffs, and the RPE and heart-rate anchors attached to each zone are conventions people drew up. Even within our own material the numbers move around: our zone calculator puts Zone 2 at ~72 to 79% of max HR, which differs from Zone 2 of the 3-zone model, and ACSM’s “moderate” intensity description is different again.

Quick correction while we’re here: we put Zone 2 at RPE 4 to 6, not 5 to 6. But again, it’s more of an approximation than anything else.

The whole point of these intensity metrics is to get the individual to do the appropriate amount and type of work to generate the desired adaptation. With that in mind, mostly everyone agrees that Zone 2 in the 5 zone model is below the aerobic threshold, and Zone 5 is above the anaerobic threshold. How you slice up the zones and prescribe/describe them can vary.

That reframes your endurance-athlete question. In a 3-zone way of counting, the ~80% easy work sits below that first threshold, which is genuinely lower RPE. In a 5-zone count, that same block splits into zones 1 and 2, with the first threshold sitting up near the top of zone 2. So “80% in zones 1-2” and “80% below the first threshold” are the same thing said two ways, and your instinct there wasn’t really wrong. The better athletes cluster that work just under the threshold rather than strolling, and it works because their volume is enormous and their easy pace is already fast. That’s a distribution for huge volume, which is a separate question from whether easy work is the best per-minute stimulus.

For 2 to 3 hours a week, the volume is too low to really worry about intensity distribution. At that volume, I’d predict higher intensity works better. Easy walking is fine as daily activity, just a weak per-minute stimulus because it is low intensity.

I’d predict much the HR/RPE mismatch is from not having a recent anchor where you went all out for a sustained period of time. I think your RPE would recalibrate . I do not think your walking is anywhere close to Zone 3. I think a 20 min field test would be useful here. In the interim, I’d use HR data.

Further reading/listening

This all comes from our three-part conditioning series, which is worth a full listen since you’re this deep in it:

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